Gob-side entry retaining mining is one of the important directions of sustainable development of coal in China.The evolution of pressure relief gas migration reservoir area in mining overburden is different from that of traditional mining methods.In order to further accurately identify the pressure-relieved gas migration reservoir area of overburden strata in gob-side entry retaining mining,the characteristics of fractures on the roof-cutting side and the non-roof-cutting side were studied by numerical and physical-similarity simulation.The dynamic development process and strain distribution law of mining-induced overburden fractures were analyzed.The method of identifying the location of pressure-relieved gas extraction target area in gob-side entry retaining min-ing was proposed,and the field implementation was carried out.The research shows that the low-position over-burden rock is affected by roof cutting and is prone to fracture and collapse,while the overburden rock cracks on the uncut side of the high-position overburden rock area are relatively developed,and the development height of the cracks on the cutting side and the non-cutting side is the same.The shape of mining-induced fractures and the strain shape of overburden rock are trapezoidal.With the periodic fracture of rock strata,the mining-induced frac-tures develop upward in a leap-forward trend.The angle of mining-induced bed separation fracture in different regions is concentrated at 0°-10°,and the angle of vertical fracture zone is mainly concentrated at 80°-120°.Based on the identification of key strata,the angle and number of mining-induced fractures,and the strain charac-teristics of overlying strata,combined with the ventilation mode,a method for determining the target area of pres-sure-relieved gas extraction in gob-side entry retaining mining is proposed.The extraction boreholes are arranged in the area of"acute angle development area of mining-induced fractures+high gas volume fraction".It is deter-mined that the extraction target area of the trial working face is 30-46 m from the vertical distance of the coal seam roof and 30-55 m from the horizontal distance of the auxiliary transportation roadway.The overall gas ex-traction effect during the mining period of the trial working face is good,indicating that the extraction borehole designed based on the determination method of the pressure-relieved gas extraction target area of the gob-side entry retaining mining is reasonable.The research results can provide some reference for the design of pressure-relieved gas extraction boreholes under the "Y" type ventilation mode of gob-side entry retaining mining.
gob-side entry retainingpressure relief gas extractionmining cracksstorage and transportation areaextraction target area
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